Lecture 20

  1. Origin
    • Arose 2.0 - 1.9 BYA
    • Eukaryotes came after:
    • - the rise of atmospheric oxygen
    • - the invention of respiratory metabolism in Bacteria
    • - the development of enzymes such as superoxide dimutase, which detoxifies oxygen radicals generated as a by-product of aerobic repsiration
    • Oldest known microfossil is ~2billion years old
    • Fossils of increasing complexity are evdident from 1.9 to 1.4 BYA
  2. Characteristics
    • Contain a membrande-enclosed nucleus, mitochondria, chloroplats (phototrophs), Golgi complex, peroxisomes, lysosomes, endoplasmic reticula, micotubules, and microfilaments
    • Includes: protists, fungi, unicellular red algae, and unicellular green algae
  3. Mitochondrian
    • Repsiratory organelle of aerobic Eukarya
    • site of respiratory enzymes and oxidative phosphorlyation
    • Cristae- internal membranes, sites of enzymes for respiration and ATP synthesis
    • Matrix- enzymes for oxidation of organic compounds
    • Evolutionary origin- falcutatively aerobic Alphaproteobacterium ~2BYA
  4. Chloroplast
    • Organelle of photosynthesis in phototrophic Eukarya
    • Stroma- lumen of chloroplast, site of enzymes of the Calvin cycle
    • Thylakoids- flattened membrane discs, site of chlorophyll and other components involved in capturing light engergy
    • Evolutionary origin- a cyanobacterium ~1.5BYA
  5. Endosymbiotic theory
    • 1. Mitochondria and chloroplasts have DNA for rRNAs, tRNAs, and respiration/photosynthesis
    • 2. Eukaryotic nucleus contains bacterial genes derived from mt and chl
    • 3. Mt and chl have their own ribosomes with 70S size like in Bacteria
    • 4. Antibiotics that kill or inhibit Bacterial 70S ribosome function also interfere with protein synthesis in mt and chl
    • 5. Phlyogenetic analysis based on 16S rRNA gene sequencing places mt and chl in domain Bacteria
  6. Hydrogensomes
    • Certain Eukarya thought to lack mitochondria have been found to have hydrogensomes
    • Found in obligate or aerotolerant anaerobes (in anaerobic Eukarya)
    • Lack enzymes of the citric acid cycle, usually lack cristae, and oxidizes pyruvate to acetate, H2 and CO2
    • Allows ATP to be made by SLP
    • Contain DNA and ribosomes and functions as a fermentive organelle
    • Metabolically degenerate mitochondria
  7. Mitosomes
    • Relic mitochondria
    • Found in some eukaryotes that lack mitochondria and hydrogensomes
    • Clustered mitochondria-like proteins surrounded by tiny double membrane sacs
    • Derived from mitochondria, but even more degenerate than hydrogensomes
  8. New Hypothesis
    • 1. Aquisition of the mitochondrian led to the origin and massive evolutionary radiation of Eukarya
    • 2. Later aquistion of the chloroplast by one of the Eukarya lineages resulted in phototrophic eukaryotes
  9. Nucleus Hypothesis
    A nucleus bearing cell spontaneously arose from an early kind of cell before the divergence of Bacteria and Archaea in response to teh increasing genome size of the early eukaryote
  10. Hydrogen Hypothesis
    A hydrogen-dependent host aquired a facultatively aerobic symbiont
  11. Chimeric Nature of Eukaryotic Cell
    • SSU rRNA gene sequence is mor similar to Archaea than Bacteria
    • Transcription/translation apparatus has many similarities to Archaea
    • Lipids are ester-linked like Bacteria
    • Energy metabolism is mor similar to Bacteria
Card Set
Lecture 20
Origin of Eukarya